It's ultimately up to you, but keep this in mind: you'll have to extend your degree an extra semester or even a year if you do Arts with the intent of transferring to Science/Laws. If you did straight science, you could gain credit for all the subjects you've done and not have to do extra work. It's just like picking up an extra degree on the side that you've yet to start. You noted that you'd prefer to pick up Arts so that you can play to your strengths, which I suppose is a good degree. I guess it depends on what kind of job you see yourself having in the sense that you could do Arts/Laws and still get to where you want to end up.
It's also worth considering the possibility that you may be forced to stick it out with the single degree you choose. I don't want to sound like a douchebag, but the L.L.B is basically the hardest degree to transfer into. If you struggled to get the ATAR required for it, it might be just as hard to transfer when you're in uni itself. If this were to happen, you'd have to stay in Science or Arts and reconsider your aspirations. However, this is just a warning, and I'm sure you're more than capable of getting in if you put in the effort, and many people have done miraculously at uni while not initially getting into their 1st preference.
Have a nice day.